The invention relates to apparatus for sawing materials into a plurality of thin slices and, in particular, to sawing brittle materials such as quartz, ceramic, or silicon.
In the prior art, a variety of saws are known, including wire saws, for cutting brittle material. One particularly useful saw is described in U.S. Pat. No. 3,824,982, which is assigned to the assignee of the present invention and the disclosure of which is hereby incorporated by reference.
As described in said patent, the wire saw comprises a wire supply means and a wire take-up means. The actual cutting mechanism comprises wire looped around a plurality of pulleys or mandrels, each having at least one groove therein, arrayed to form a cutting zone. The saw also comprises a wire storage means having a sliding carriage, with at least one pair of pulleys thereon, mounted between a corresponding pair of fixed pulleys. Wire from the supply means follows a path through the storage means and the plurality of pulleys in the cutting mechanism to the take-up means. A reversible motor drives one of the plurality of pulleys in the cutting mechanism, causing the carriage in the wire storage means to move back and forth horizontally along the rail or track to which it is mounted. As the carriage reaches the end of its travel, the motor is reversed, thereby reversing the direction of the carriage.
The system may also include suitable sensing and adjusting means, eg. for wire tension, direction, and feed rate. In the particular application of cutting wafers from a silicon ingot, the system also includes means for applying and removing a suitable slurry coating for the wire.
As useful and productive as the wire saw described in the above noted patent is, it is desired to improve its capacity at least in terms of the cutting rate. In the semiconductor industry, this is particularly important since the diameter of the silicon ingots from which wafers are cut has increased. The increase in diameter, assuming the same width kerf, changes the volume of material which must be removed in proportion to the square of the change in diameter. Thus, a twenty-five percent increase in diameter causes a fifty-six percent increase in volume. If the cutting rate were unchanged, the number of wafers per hour from the wire saw would be reduced in proportion to the increase in volume. One is thus confronted with the choice of buying additional equipment or improving existing equipment.
In view of the foregoing, it is therefore an object of the present invention to improve the cutting rate of a wire saw.
Another object of the present invention is to improve the operation of the wire storage means of a wire saw.
A further object of the present invention is to provide a wire saw of simplified construction.